In the manufacture of containers such as glass bottles and jugs, various types of anomalies can occur in the sidewalls, heels, bottoms, shoulders, necks and/or finishes of the containers. These anomalies, termed "commercial variations" in the art, can affect commercial acceptability of the containers. It has been proposed to employ electro-optical inspection techniques for detecting commercial variations that affect the optical properties of the containers. The basic principle is that a light source is positioned to direct light energy onto the container, and a camera is positioned to receive an image of the portion(s) of the container illuminated by the light source. The light source may be of uniform intensity, or may be configured to have an intensity that varies across one dimension of the light source. Commercial variations in the portion of the container illuminated by the light source are detected as a function of light intensity in the image of the illuminated container received and stored at the camera.
U.S. Pat. No. 4,945,228, assigned to the assignee hereof, discloses an apparatus for inspecting the sealing surface of a container finish, which includes a light source positioned to direct light energy onto the container sealing surface as the container is held in stationary position and rotated about its central axis. A camera, which includes a linear array or matrix (area) array of light sensitive elements, is positioned and oriented with respect to the container axis of rotation to receive light energy reflected from the sealing surface, with the camera having an effective field of view limited to an angular portion less than the entire circumference of the container sealing surface. The camera array is scanned at increments of container rotation to develop information indicative of intensity of light at each array element as a function of such increments, and commercial variations at the container sealing surface are detected as a function of such information. The apparatus so disclosed is well adapted to detect commercial variations that affect reflectivity of the container sealing surface, such as line-over-finish variations, blisters, stones and a dirty container finish.
U.S. Pat. No. 5,489,987, also assigned to the assignee hereof, discloses an apparatus for inspecting the sealing surface area of a container, which includes a light source positioned to direct a narrow beam of light energy at an acute angle onto the sealing surface area of a container as the container is rotated about its central axis. A light sensor is disposed to receive the narrow beam of light energy reflected from the sealing surface area, and provides an output signal that varies as a function of position of incidence of the reflected light beam on the sensor. That is, the reflected light beam is incident on the sensor at a position that varies with height or level of the sealing surface with respect to the light source and sensor, and the sensor is characterized by providing an electrical output signal that varies as a function of position of incidence of the reflected light beam on the sensor. Variations in height at the sealing surface area are detected as a function of the sensor output signal. In one embodiment, light source/sensor pairs are disposed on diametrically opposed sides of the container axis, and warp, dip and/or cock at the sealing surface of the container is detected as a combined function of variations in position of incidence of the reflected light beams on the sensors as the container rotates.
Copending U.S. application Ser. No. 08/856,829, also assigned to the assignee hereof, now U.S. Pat. No. 5,896,195 discloses a method and apparatus for inspecting the sealing surface of a container. In one embodiment, first and second light sources direct light energy onto the sealing surface of a container from differing angles with respect to the container axis and the nominal plane of the sealing surface. Light energy reflected by the sealing surface area of the container from the first and second light sources is directed onto an area array sensor in such a way that the sensor effectively views the container sealing surface area from two differing angles corresponding to the angles of illumination from the light sources. The differing light sources are of differing structure or nature for illuminating the sealing surface with light having differing properties as well as differing illumination angles for detecting differing physical and/or dimensional characteristics of the container sealing surface. The light sources are alternately energized, and the area array sensor is scanned to develop sequential two-dimensional images indicative of differing sealing surface characteristics. Inaccuracies can arise associated both with container movement between sequential frame scans and ambient light incident on the area array sensor during each image frame. When the subject matter of this copending application is implemented at the so-called cold end of the container manufacturing process, at which the container is held in stationary position and rotated about its central axis, the container will not only undergo finite rotation between sequential frame scans, but also may wobble laterally between sequential frame scans. Likewise, when implemented at the so-called hot end of the manufacturing process, at which a container is moved in a direction transverse to its axis beneath the inspection apparatus, the container sealing surface (or other area being inspected) will move a finite distance between sequential frame scans. It is important in obtaining reliable inspection information to minimize the effects of both container movement and ambient light during the inspection operation. It is a general object of the present invention to provide a method and apparatus for container inspection in which one or both of these objectives are accomplished.